This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A094157 #12 Nov 08 2022 08:06:51 %S A094157 2,12,202,9468,836017,111255228,20433309147,4940118795869, %T A094157 1520564059349452,580578894859915650,269291841184184374868, %U A094157 149146250420586942401004,97222048664558428304285193,73681349947834075264704425280,64240926985765124116695616020874,63847923667734462963941294951243328 %N A094157 Bisection of A000940. %H A094157 S. W. Golomb and L. R. Welch, <a href="http://www.jstor.org/stable/2308978">On the enumeration of polygons</a>, Amer. Math. Monthly, 67 (1960), 349-353. %o A094157 (Python) %o A094157 from sympy import factorial, divisors, totient %o A094157 def A094157(n): return 2 if n == 2 else ((sum(totient(m:=(r:=n<<1)//d)**2*factorial(d)*m**d for d in divisors(n<<1,generator=True))+(1<<n-2)*r*(r+6)*factorial(n))>>2)//r**2 # _Chai Wah Wu_, Nov 07 2022 %Y A094157 Cf. A000940, A094156. %K A094157 nonn %O A094157 2,1 %A A094157 _N. J. A. Sloane_, May 05 2004